Not many buildings start with an in-situ concrete structure on the lower floors and switch to precast higher up – but there’s very little that’s off-the-peg about the new London College of Fashion (LCF). This is highly bespoke structural tailoring, pieced together with exactly as many types of concrete component as it needs.
Its hybrid structure is quite fascinating, featuring both post- tensioned in-situ concrete floor slabs, and pre-tensioned precast ones. It has precast cladding, and a spectacular in-situ concrete curving staircase (see box, below). Here and there are steel-encased-in- concrete columns (and beams), while some of the lower levels contain massive reinforced concrete transfer structures that would be more at home in a bridge. On the tenth floor, we find in-situ-filled precast shell beams.
“It’s about using a pallet of materials where they are most appropriate,” says Emily McDonald, project principal with engineer Buro Happold. “It’s a real smorgasbord of techniques and we’re using this wide range of off-the-shelf components. But I love that it doesn’t read like that at all. It reads like the whole that it is.”
It is important that it does because, architecturally, the LCF has competition. It is just a short walk from the concrete swirls of the Zaha Hadid-designed Olympic Aquatic Centre (CQ 241) and sits between three other notable new buildings: the V&A East, BBC Music and Sadler’s Wells East. All four are part of the Stratford Waterfront East Bank, a new cultural quarter rising across the river from the former Olympic stadium.
The 36,000m2 LCF easily holds its own in this company. At 15 storeys, it is the tallest, and its precast-clad exterior presents a confident industrial aesthetic which, if hardly unusual these days, is deployed here with a very considered rationale. The LCF comprises a number of schools that have developed over time in different locations, and this building brings them all together for the first time, explains Alex Wraight, partner with architect Allies and Morrison. “We visited the existing sites expecting to find art-school chaos, but we discovered fashion isn’t like that,” he says. “It was more cutting tables and serried ranks of sewing machines. There was a lot of making and producing going on, more like a factory. So the new LCF has something of the textile mill about it.”
The building is styled this way for practical reasons too. “The client wanted a 100-year- plus lifespan, and it has to be able to adapt and easily accommodate different fit-out scenarios to stay relevant and useful. So, like a mill, we have high ceilings, plenty of natural light, and a structure that allows large areas of free space to be organised or compartmentalised in different ways.”
This requirement for flexibility, says Wraight, was key in the decision to use concrete: “A steel frame with linings would be much more complicated to take apart and reconfigure than the exposed concrete ‘structure as finish’ approach we’ve taken here. And of course this also cuts the costs and carbon content associated with linings.”
Other advantages offered by concrete include the ability of the exposed frame to conserve or absorb heat: “That helps lower heating and cooling costs over the entire life of the building.”
Concrete is also tough, he adds: “You need that in a building accommodating 6,000 students. You can see from the way university buildings of the 1960s have aged that concrete just gets better and develops character over time. It’s got soul.” The LCF’s massive cuboid proportions certainly have a mill-like aesthetic, subtly accentuated by detailing. Its precast cladding consists of 900 single-skin, grit- blasted panels covering 11,323m2, the texture of which has been likened to needlecord. “We opted for horizontal patterning for these vertical elements, to suggest the warp and weft of fabric,” says Wraight. “The pattern edge is visible from the inside, where the brick-sized scallops give a human-scale interest, but it also registers from 500m away.”
But why the plethora of concrete types? Having started off in-situ, would it not have made sense to continue? Ellie Moore, senior structural engineer with Buro Happold, explains how the building is arranged in zones, with different construction techniques being deployed to meet the requirements of each.
“The building sits on 250 piles, 750-900mm in diameter and between 20-25m deep. The first four levels contain more special, bespoke spaces, including the entrance areas and the curving concrete staircase which rises from basement level to the fourth floor – so it made sense to construct all these from in-situ concrete to achieve the monolithic character that the architect wanted.”
But above level four, the floor plates become more repetitive: “The precast approach, with its ability to reuse moulds and produce identical elements, made it simple to replicate the structure. That helped with programme efficiency too, which was vital as the LCF is the largest building on the waterfront and was very much on the critical path for the whole East Bank development.”
The in-situ floor slabs on the lower levels are post-tensioned to help lengthen spans where required, while retaining a relatively light 300mm depth: “This saves the carbon cost of thicker concrete and reduces the loading on the whole building, so saving on foundations too,” says Moore. “Further carbon reductions have been made by using a 50% GGBS mix in the foundations and between 30-40% in the superstructure where setting times were more critical to the programme.”
The LCF’s column structure is quite unusual, again reflecting the structural needs of the different zones. While the footprint is almost 60m x 60m, the square centre of the building, known as the heart space, is a 36 x 36m area where both air and people can circulate, containing lifts, bathrooms and risers for the services. It is constructed and defined by 46 rectangular columns, 1m x 0.6m. Connected at each level by a 750mm-deep ring beam, these lend the building stiffness and stability. Within sections of the heart space is a 6m grid of slimmer columns to allow lightweight spans where clear soffits are not required.
Outside of the heart space’s inner square are the workshop and studio areas. These are created by spanning out from the rectangular columns to the perimeter. Each of the four sides has a different span (9m, 10.5m 12.9m and 13.5m) resulting in spaces that suit various activities. “It was important they had clear soffits to help them remain flexible,” says Moore. “Given the spans, the most efficient way to achieve that structurally was with pre-tensioned precast hollowcore planks.”
More normally seen in car parks, the hollowcore slabs proved a light, inexpensive solution that also helped facilitate the rapid programme. At the perimeter, these rest on a ring beam supported every 3m by thermally broken columns that are trapezoidal in section. The cladding hangs off the exterior face, which is wider than the inside – 1m compared to just 600mm. “The shape creates natural shading to limit solar gain, then inside, we have used the 1m depth of the columns to create deep window reveals,” says Wraight.
This feature was inspired by similarly deep reveals at one of the LCF’s existing premises. “We saw how useful they were,” he says. “You can sit and chat, sew in natural light, hang fabric up to dry – they were really well used, so we’ve imported the idea to the new building with window seats between the perimeter beams.”
Such user-friendly details maintain a human scale amid some pretty sizeable chunks of concrete – such as the shell beams at level ten. Moore explains that these were needed because the building steps in at this level: “The shell beams are transferring loading from columns above. In this location, the architectural intent was for the soffit of the beams to be precast to achieve the same finish as precast slabs. But these beams are 14m long and 1m deep, and solid precast beams that size would have exceeded our crane’s lifting limit of 10 tonnes.”
Buro Happold’s ingenious solution was to use precast shell beams, which are hollow U-shapes in section: “These were light enough to be lifted into place and then they were filled with reinforced in-situ concrete to achieve the required strength.” Even larger transfer structures in the in-situ part of the building could be more traditionally constructed. One, spanning over the basement- level auditorium, is 2.8m deep to enable it to support the loading of the 14 floors above.
Concrete on the catwalk
The LCF’s spectacular curving concrete staircase rises from its basement level to the fourth floor and is the stand-out feature of the building’s interior. “It’s designed as an invitation, an unfurling, experiential journey,” says Alex Wraight, partner with Allies and Morrison.
“As the sculptural focus, it represents quite an investment – but it was never on the value- engineering list.”
The without-compromise approach has paid off: “It’s brilliant to see the students using it as a catwalk and featuring it along with their designs on Instagram,” he says. “Yes, there are less carbon-intensive ways of getting from one floor to another – but this adds so much to the experience of the building and will really last. A steel and timber staircase would need more maintenance and possible replacement after a couple of decades.”
The stair was designed on Revit, but with the help of Enscape: “It’s essentially a game engine that allows you to virtually walk around your model. But the result is really testimony to the craftsmen who made it. As you can imagine, the formwork was extraordinary.”
Paul Greaves, director of bespoke formwork specialist 3D Pattern and Mould Makers, explains how it was done: “First of all we 3D-printed some small models of the stairs so we could think about how best to proceed. In the end, the formwork for each staircase was made in sections or pods. One of the flights, for example, had 13 pods. So we would complete the first three pods and check the assembly and fit in our factory before sending off pods one and two. We would then make pods four and five before delivering pods three and four. That way we could be sure the fit was always perfect, all the way up.”
The staging and framework for each pod was CNC cut and assembled before the curving moulds for the balustrades were formed from top-grade birch-faced plywood. “We used 6mm ply as it was thin enough to bend, but three layers of it – so 18mm in total – to achieve the strength needed for the weight of concrete.”
The soffits were mostly formed in a similar fashion, adds Greaves: “Though where the curve radius was particularly tight, CNC- machined MDF was used to achieve the correct gradient and curvature.”
Once assembled on site, Expanded would pour the balustrades first and then remove the inner formwork before pouring the soffit. The steps were created later by fixing new formwork to the struck concrete and pouring a few steps at a time.
The impressive colonnade at the front of the LCF is another example of how the engineers have used a multi-component approach to achieve an impressively integrated aesthetic. The columns are 15m high and trapezoidal in section and slimmer at the base than the top. “They bear the weight of the building above so have to be very strong,” says Moore. “They are 1.5m deep at the base but 2.75m at the top, and each is constructed from steel I-sections which were erected first, a bit like a vertical truss. This then had reinforcement attached before adding the concrete, poured in several sections.”
The five columns are each connected to the building by beams made from more steel sections encased in reinforced concrete. Spanning between these beams to make the ceiling of the colonnade are the same kind of pre-tensioned hollow-core precast planks used within the upper floors of the building interior.
The LCF exceeds the London Legacy Development Corporation’s target of reducing embodied carbon (compared to Stage 2 baseline) by 15%, and has also achieved BREEAM Outstanding – facts that Wraight believes might surprise some. “Questions have been raised about the embodied carbon content, but with the structural approaches we have taken, together with the use of GGBS, we have been able to reduce that quite a bit.”
Perhaps more importantly, he adds, it really does matter how well the building will last – both physically and in terms of its usability. This mirrors a broader sea-change in the fashion industry, which is turning against cheap, wear-and-throw- away “fast fashion”. “The LCF itself champions the idea of slow fashion – that it is better, environmentally, to invest in long-lasting materials and designs to create clothes that will last,” says Wraight. “The new LCF is just that: slow fashion.”